1) Are you sure that "<?=MOLLY.'update.php'?>" is giving you the correct URL? - Check the HTML source the PHP renders. Check whether you need a leading / or not. 2) Is #submit a submit button in a form or a hyperlink? If it is, you'll need to cancel the default event occuring (accept the event object as the first parameter, and then call event.preventDefault()).
–
MattJan 6 '12 at 11:36

Use firebug in Firefox to check the AJAX request - that would be first place to check.
–
BruceJan 6 '12 at 11:38

Instead of "if ($_POST)" you should use "if(isset($_POST['stitle']))".
–
cillosisJan 6 '12 at 11:38

Is that short tags "<?=" is working?
–
Muthu KrishnanJan 6 '12 at 11:38

molly is the right url and the submit is a <span> thanks though
–
TinyJan 6 '12 at 11:39

and see if the message is returned and logged in the console.
If it is, check your $_POST by echoing back the values you sent, also echo back your email variable to see that it outputs correctly.

If it all works fine, you need to check if your server is set up correctly for the mail command to actually be able to send an email, as the problem is most likely serverside when everything else is eliminated.

Oh, and you should do what cillosis says, use isset and check something in the $_POST superglobal, not just a if($_POST), but since your running the mail function before that in your PHP, that's probably not your main problem.